In the manufacture of propylene homopolymers and copolymers, conventional polymerization techniques using unsupported catalysts result in the simultaneous production of substantial quantities of atactic polymer in addition to the desired product of high crystallinity and isotacticity. Various methods have been employed for the purification and separation of these two polymers. The by-products, i.e., the atactic polymer of low crystallinity is being utilized commercially as a component in various adhesive compositions, roofing materials, caulking compounds, etc.
Recently, developments have been made of new catalysts which are highly active and more stereospecific than the afore-mentioned conventional catalysts. The proportions of atactic polymer in the polymers produced employing these catalysts are substantially reduced and therefore the polymer product generally does not require any purification for removal of the atactic or low crystalline polymer. Because of the rapid adaptation of existing polymer facilities to the use of these new catalysts, there has been generated a serious shortage of low-crystalline, atactic polymers.
U.S. Pat. No. 3,789,036 to Longi et al. discloses a process for the production of ethylene-propylene elastomers containing between about 20 and about 70 wt. % ethylene using a magnesium-supported titanium catalyst, e.g., a co-ground mixture of titanium tetrachloride and magensium chloride. It has been found that this catalyst is not very active and, therefore, the polymer produced in the process contains undesirably large quantities of catalyst residues. Secondly, the polymer is more crystalline than desired as measured by the m/r ratio described in detail hereinafter. Finally, because of the low catalyst activity, the catalyst costs become prohibitive.
It is therefore an object of the present invention to provide a highly efficient, novel process for the production of substantially amorphous polymers of propylene and ethylene.